This invention relates to a sewing machine which sews upper and lower cloth pieces having the same pattern on the two cloth pieces while maintaining correct alignment of the pattern.
Generally, in a conventional sewing machine, a skilled working must spend many hours and take great care in sewing together two cloth pieces having the same pattern to form the back body of a blazer for either a gentleman or a lady or to fasten the parts of sleeves to the shoulders of the blazer body while maintaining correct alignment of the pattern.
U.S. Pat. No. 4,612,867 discloses a sewing machine for performing pattern-match sewing. The sewing machine has two sensors one for the upper cloth and another for the lower cloth, detects intensity of light from each cloth with the sensors and generates intensity curves for each cloth. The sewing machine determines displacement between the two cloth by comparing the intensity curves and adjusts a feed pitch of the upper cloth in order to align patterns of the cloth pieces based on the displacement.
The upper and lower cloth pieces each having both a lateral pattern and a vertical pattern thereon, e.g. having a check pattern, are sewed on the bias against the patterns as shown in FIG. 22. In this case, an end of the lateral pattern passes over a detector much faster than that of the vertical pattern. FIG. 23A shows detected data corresponding to the vertical pattern and its data curve has broad peaks. FIG. 23B shows data detected, on the other hand, corresponding to the lateral pattern and its data curve has sharp peaks. The pattern matching of the two cloth pieces is usually conducted by either matching the vertical or lateral pattern on the two pieces in alignment. When the vertical pattern, however, is used for the pattern matching, there is some difficulty because of its unclear and vague broad peaks.